The invention relates generally to magnetic tape carriage assemblies and more particularly to tape head mounting means therefor. More specifically still, the invention relates to improved adjustable tape head mounts.
The use of magnetic tape for recording and playback of data in electronic form is well known. In such recording and/or playback systems, a magnetic tape is caused to move relatively across the face of a transducer or tape head for the purpose of either receiving electrical signals from the tape head and storing them on the tape in magnetic form or, alternatively, for using the movement of such recorded magnetic signals past the tape head for inducing electrical signals in the tape head and its associated circuitry. Typically, the magnetic tape is stored on one reel and is collected on a motor-driven second reel. The normally stationary tape head includes one or more magnetic pole pieces in turn connected to appropriate input of output electrical circuitry. The relative motion of the tape past the tape head pole piece(s) causes magnetic interaction therebetween when data appears on either one, such that said data is transferred as well to the other.
To obtain good fidelity of the data stored or played back, considerable attention must be given to stabilizing the speed of the tape past the tape head and also to maintaining correct alignment and placement of the tape head pole pieces relative to the tape. These efforts may take on particular importance when the data being stored and/or played back is of a biomedical or physiological nature, as for instance the electrical waveform data obtained by monitoring a human heart as with the technique of ambulatory (Holter) cardiography. Specifically, electrodes are appropriately placed on an ambulatory patient and connected with a small lightweight, very slow-speed recorder which is worn by the patient for many hours, for instance one full day.
An example of the drive mechanisms associated with such a slow-speed recorder is described in U.S. Pat. No. 3,913,860 issued Oct. 21, 1975, for SLOW-SPEED TAPE RECORDER MECHANISM by Richards. That patent directs particular attention to the attainment of highly uniform tape speed. It will be appreciated, however, that the elevation and angular orientation of the tape relative to the tape head pole pieces as it is drawn therepast will affect the character of the signal transferred from one of the elements to the other. This becomes more evident when it is understood that the width of a pole piece is typically 0.020 inch and the width of a track of data stored on the tape is 0.020 inch and that the two must be aligned and maintained in register within 0.0005 inch. Unless the elevation and angular orientation of the tape head pole pieces relative to the tape is maintained within these limits throughout recording and playback, some distortion and thereby loss of the information will occur.
In order to minimize or eliminate such losses, efforts have been made initially to obtain and then to maintain the optimum orientation of the tape head pole pieces constant relative to the tape throughout a recording or a playback operation. Moreover, the tape head mounting mechanism has been provided with some degree of adjustability so that repeatability between the recorded signal and the signal played back may be obtained, as by a calibration operation at the initiation of the playback of the recorded signal. Such adjustment and calibration sometimes recognizes some form of standardized signal recorded on the tape to allow an operator to adjust the tape head mounting mechanism such that the reproduced signal substantially conforms with the recorded reference signal.
One example of such an adjustable tape head mounting mechanism is to be found in the Models 6002 and 6004 Holter Scanners marketed by American Optical Corporation. That tape head mounting mechanism provided a pair of opposed clamps for embracing and retaining the tape head. The lower one of the pair of clamps rested on an "M" shaped spring, and a pair of adjustable mounting screws extending through one of the clamps and into engagement with the head carriage served to adjustably urge the clamp and head assembly into compressive engagement with the spring. By selective adjustment of the screws, some control of the elevation and angular orientation of the tape head and its pole pieces relative to the tape was obtainable; however, the quality of adjustability and resulting stability of the tape head and its pole pieces were less than optimum for such physiological recording systems. For instance, the adjustment screws are in a single plane spaced well to the rear of the tape head's pole pieces, and only slight aberrations in the contact surface of an adjustment screw may act on the head clamp to produce, in addition to the attempted and desired adjustment, an unwanted displacement of the clamp and tape head. This unwanted displacement is small and has a given angular sign adjacent to the head of the screw but is magnified and can have the opposite sign at the pole pieces because of the leverage arm between the pole pieces and the screw head.
Accordingly, it is an object of the present invention to provide an improved adjustable tape head mounting mechanism.
It is another object of the invention to provide an improved adjustable tape head mounting mechanism which is relatively easy to adjust yet affords a high degree of accuracy and stability in its positioning, and thus the positioning of the pole pieces, relative to the tape.